China's building energy consumption has accounted for 27.8% of the total social energy consumption, and the energy consumption of heating and air conditioning accounts for 55% of the building energy consumption. In modern buildings, the area proportion of glass in the outer walls is getting higher and higher. It has been measured that heat transfer through glass windows accounts for 48% and 71% in winter and summer, respectively. Where an air conditioner is used to adjust the indoor temperature, as the cooling temperature increases by 2° C., the cooling load will decrease by 20%; as the heating temperature decreases by 2° C., the heating load will decrease by 30%. Energy consumption can be significantly reduced by attaching a heat-insulating film or coating a heat-insulating coating on the glass.
At present, heat-insulating films or coatings on the market still focus on the performance of blocking infrared ray without the ability to respond to environmental change. They merely have the function of reflecting infrared light rather than transmitting the infrared ray at low temperatures, being unable to play a role in adjusting the temperature difference between indoors and outdoors intelligently. Therefore, a material must be found that is able to adjust solar heat intelligently, so as to make the inside of buildings warm in winter and cool in summer.
Vanadium dioxide materials have a first-order phase transition property, being able to sense a change in ambient temperature, and intelligently respond to the change to realize the selective transmission or shading for the spectrum of sunlight. Generally, when the ambient temperature is lower than the phase transition temperature, a film or coating containing vanadium dioxide is almost completely transparent for visible light and mid-infrared light of the sunlight; when the ambient temperature exceeds the semiconductor-metal phase transition temperature, vanadium dioxide performs a phase transition and turns to R (rhombohedral) phase. At this time, the material can selectively shade the mid-infrared light, and achieve the purpose of being transparent (allowing the visible light to transmit) and insulating heat. The semiconductor-metal phase transition of vanadium dioxide is a heat-induced reversible change, and the temperature-switching effect can be used for intelligent control for transmitting and blocking mid-infrared rays. By the advantage of low transmission at high temperatures and high transmission at low temperatures in the infrared region of vanadium dioxide, an energy saving window system of full intelligence can be prepared.
Optical calculation indicates that (S.-Y. Li, G. A. Niklasson, and C. G. Granqvist, Nanothermochromics: Calculations for VO2 nanoparticles in dielectric hosts show much improved luminous transmittance and solar energy transmittance modulation, JOURNAL OF APPLIED PHYSICS 108, 063525 2010) if vanadium dioxide nanopowders are dispersed into other substrates such as transparent macromolecules, the visible light transmittance can be improved to a practical level in addition to keeping the optical control property of vanadium dioxide, by which energy saving reconstruction for glass, wall space, and outer walls of transportation such as vehicles and ships in service can be carried out. A coating material for intelligent temperature control can be prepared by making the vanadium dioxide materials into nano-size and composited with organic modifying materials. However, due to their small specific surface area and high surface free energy, the nano-particles tend to aggregate with each other, which determines that when vanadium dioxide nano-particles are directly added into coating material, they hardly perform as nano-materials, and tend to aggregate with each other, which has an influence on the optical properties and appearance of the coating, thereby limiting the application of the material on glass films and transparent glass. For example, Chinese patent application No. 200410051965 refers to a vanadium dioxide coating material for intelligent temperature control, however the vanadium dioxide particles referred to belong to unmodified vanadium dioxide particles, and do not relate to the pretreatment for the particles, especially the pre-dispersion treatment for the vanadium dioxide particles referred to in the present invention, and the improvement of dispersibility and chemical stability due to the organic modification treatment.
Chinese patent application No. 200610117027.4 refers to a method for preparing vanadium dioxide suspensions, and relates to dispersion treatment for vanadium dioxide powders; however, this treatment adopts an inorganic modification method, which is substantially different from the preparation of vanadium dioxide composite particles by an organic modification method. Additionally, this invention adopts an acidic or alkaline condition, which would destroy the structure of vanadium dioxide.
Chinese patent application No. 200980123044.0 (with of title of thermochromic microparticles, dispersions thereof, and manufacturing method thereof, as well as light-modulating coating materials, light-modulating films and light-modulating inks) refers to a surface treatment for dimming painting particles; however, it does not present the specific modification method, and the treatment objects of this invention are composite particles of titanium dioxide and vanadium dioxide, which are substantially different from the vanadium dioxide composite particles in the present invention.
Chinese patent application No. 200810033032.6 refers to a film for intelligent thermal insulation and the preparation method thereof, however, it does not relate to the organic modification pre-dispersion treatment for VO2 particles, especially the particles referred in the present invention. In the present invention, the organically modified vanadium dioxide powders have greatly improved dispersibility after modification treatment, especially the treatment with silane coupling agent, and can play the role of nano-materials indeed, which is close to the results of theoretical calculations, and the prepared coating for intelligent temperature control has a notable improvement of control performance for infrared light, which is close to the results of theoretical calculations.
Chinese patent application with publication No. CN101265374A discloses a vanadium dioxide high polymer film for intelligent temperature control under solar heat, which is prepared by adding vanadium dioxide to a polymer film directly. However, the coating of the present invention is prepared by a coating method, and the prepared coating of the present invention is of higher transparency, lower haze, and excellent performance.